1. Field of the Invention
The present invention relates to a tightening device that is able to tighten a fastening member such as a bolt or a nut using a plurality of tightening processes.
2. Description of the Related Art
In order to increase the accuracy with which fastening members such as bolts or nuts are tightened, a known tightener measures the tightening torque that acts on the fastening member, and is numerically controlled to end the tightening when the measured torque reaches a set torque (e.g., see JP 2013-166211A).
Also, additional tightening that involves torque being further applied to tighten a fastening member that has already been tightened is performed in some cases (see JP 2013-166211A).
There is a need for a way of checking whether tightening has actually been performed to a desired set torque or greater, after a fastening member has been tightened or after additional tightening has been performed.
In tightening the wheel nuts of a vehicle, the wheel nuts are firstly tightened and run in, and then loosened and tightened again in order to check whether tightening has been performed to a prescribed set torque. Further running in thus needs to be performed when wheel nuts that have already been tightened once are loosened and retightened, making it difficult to determine whether the tightening torque has really reached the set torque.
An object of the present invention is to provide a tightening device that is able to check that a fastening member has been fastened to a desired set torque or greater after being tightened, without loosening the fastening member.